In recent years, means for rapidly transmitting information have undergone marked development, making it possible to transmit data and images comprising huge amounts of information. As data transmission technology has improved, the need for higher density recording in the recording media and recording and reproduction devices used to record, reproduce, and store information has developed.
In addition to using microgranular magnetic materials, it is known that dispersing microgranular magnetic materials to a high degree and increasing the smoothness of the magnetic layer surface are effective means of achieving good electromagnetic characteristics in the high-density recording region. A magnetic recording medium with a high degree of gloss can also be achieved by increasing the dispersibility of the magnetic material. For increasing the smoothness of the magnetic layer surface, it is also effective to improve dispersibility of nonmagnetic powders in a nonmagnetic layer positioned below a magnetic layer.
As described in Japanese Unexamined Patent Publication (KOKAI) No. 2003-132531 or English language family member US 2003/0143323 A1, for example, one widely employed means of increasing the dispersibility of the magnetic material is to incorporate a polar group such as SO3Na into the binder. The contents of these applications are expressly incorporated herein by reference in their entirety. Phosphonic acid, phosphoric acids, and the like are known additives that effectively enhance dispersion.
One effective means of improving dispersibility is to incorporate a polar group into the binder (polymer) to cause it to effectively adsorb to the surface of magnetic powder and the like. However, when an excessive quantity of polar groups is incorporated into the binder, dispersibility sometimes diminishes. Accordingly, the use of a dispersing agent is conceivable. However, the dispersion-enhancing effect achieved by the above-described phosphonic acid, phosphoric acids, and the like is inadequate. Further, the use of a dispersing agent to increase the dispersibility of the magnetic layer necessarily causes a decrease in the density of magnetic material in the magnetic layer, and is thus undesirable from the perspective of achieving high density.